Abstrakt
At the high luminosities envisaged for the new Super Flavour Factory - SuperKEKB, the detection system closest to the beam pipe - a new Belle II silicon vertex detector will have to face an extremely harsh beam-related background and, consequently, high hit event rates, but still provide precise measurements of primary and secondary decay vertices. During the design phase of the vertex detector, consisting of two layers of pixel sensors and four layers of double-sided microstrip sensors, one has to carefully take into account all available technological options and optimise the detector design to fully reach the expected physics performance.
For that reason we have initially utilized a modular design of ILC software framework and used it in full MC simulations for multi-parameter studies. In this paper we present the description of the Belle II vertex detector, our approach to the multi-parameter optimisation studies and finally, the obtained results: the detailed study of the expected material distributions of the vertex detector; optimisation study of the pixel detector layout with the final determination of the most optimal configuration; the influence of the slanted microstrip detectors in the forward region on the detector in-plane resolution and hit occupancy; and the expected impact parameter resolutions using or not using the two innermost pixel layers (to demonstrates the improvement of impact parameter resolutions by implementation of pixel sensors at Belle II).
For consistency, the software chain has been validated against the official Belle software framework and cosmic muons data taken at Belle.